The present application relates to antireflective compositions and methods of using the same.
With the introduction of aliphatic polymethacrylate resist polymers in ArF/193 nm photolithography and the decrease of the resist thicknesses due to transparency, and depth of focus reductions at high numerical aperture (NA), the resist pattern itself was found to no longer be a suitable mask for its transfer into the substrate via reactive-ion etch (RIE) processes (e.g., Lassig, S., et al., Solid State Technology 45(10), 48-54, 2002; Hudson, E. A., et al., Proc. Dry Process Int. Symp. 253-258, 2003). Consequently, the trilayer scheme was introduced in which a Si-containing layer (silicon-containing antireflective coating (SiARC) or Si oxide) is coated/deposited on top of an underlayer/organic planarizing layer (UL/OPL), e.g., Burns, S., et al., Proc. SPIE 6153, 61530K-1-61530K-12 (2006). These layers have alternating selectivity towards fluorine and oxygen-containing RIE chemistry, and therefore, allow for highly selective pattern transfer from the aliphatic photoresist pattern on top of the SiARC into the substrate below the UL. Lastly, the OPL/SiARC layer combination has played an important role for reflectivity control in high NA optical lithography applications.
An important function of the SiARC is their excellent etch resistance against oxide-containing etch chemistry, which enables them to act as an etch mask to transfer the pattern into the OPL. As SiARCs are typically based on organo-functionalized silanols that crosslink to form a silyl-ether network, this etch resistance depends on the content of silicon in these materials: earlier generation SiARCs contained only 17% Si, while most SiARCs used for ArFi trilayer stacks contain 43% Si. Generally, the more Si in the SiARC, the better its etch resistance. The reason for the good etch resistance against oxygen-containing etch chemistry is believed to be due to the non-volatility of SiO2 that typically forms a protection layer around the bulk of the SiARC during the O2-containing OPL open etch. Due to the silyl-ether networks in these SiARCs, these SiARCs are not easily strippable.
The non-volatility of SiO2 limits the options to remove the SiARC during wafer rework processes. Most often, since SiF4 is volatile, aqueous HF or F-containing dry etch chemistry (CF4, CHF3, etc.) are used. However, both HF and CxFy species not only react with the SiARC but also with substrate materials like silicon oxide, silicon nitride, or in case of CxFy, also with Si.
Another option to remove SiARCs using wet chemistry is based on formulations of tetraalkylammonium hydroxides, typically tetramethylammonium hydroxide (TMAH), in mixtures of organic solvents and water. Typically, TMAH concentrations greater than 1 wt % are being used. For SiARCs with 43% Si, even greater than 5 wt % TMAH can be used. These high concentrations of TMAH not only bring the risk of substrate damage (highly concentrated TMAH also dissolves Si) but also raise significant toxicity concerns, particularly if organic solvents (e.g., dimethyl sulfoxide, i.e., DMSO) are used that facilitate the transport of organic material into the human body.
SiARCs with very low Si content (17%) can sometimes be wet stripped with “piranha acid” (conc. H2SO4+30% H2O2). As some integration schemes use titanium oxide or nitride as substrates, these can also react/dissolve with such, as H2O2 forms a soluble peroxo complex.